RU2301505C2 - Method and device for restoring a call in wireless communication system - Google Patents

Abstract

FIELD: wireless transmission of speech and data, possible use in wireless communication device for restoring a call.

SUBSTANCE: in accordance to method, when a communication line between base station and mobile station is interrupted, mobile station and infrastructure set up potential emergency restoration base stations. Base station of original cell contacts all neighbors capable of call restoring as potential emergency restoration base stations. Call restoration operation is considered to be emergency restoration operation. Mobile station sets up soft service transfer for emergency restoration base station, and uses default channel and alternative channel during that. When service transfer is finished, emergency restoration base station stops using the channel by default.

EFFECT: increased call restoring reliability.

2 cl, 13 dwg

Description

FIELD OF THE INVENTION

The present invention relates to wireless voice and data transmission. In particular, the present invention relates to a new and improved method and apparatus for call recovery in a wireless communication system.

State of the art

A wireless communication system typically includes multiple base stations (BS) (BS), each of which is associated with a cell and / or sector that communicates with multiple mobile stations (MS) (MS). Base stations are controlled by a base station controller (BSC) (BSC). As the mobile station moves through the system, the quality of the signals received from the base stations fluctuates. When the communication line between the base station and the predetermined mobile station deteriorates, it is possible to prevent the loss of communication by establishing a communication line with at least one more base station. To initiate such an alternative communication link (s), a handover process is provided. In a handover situation, the infrastructure negotiates with various base stations and this mobile station. However, often the signal quality degrades too quickly to be matched.

Therefore, there is a need for a method and apparatus for restoring a call in various situations. Further, there is a need for a reliable call recovery method in a wireless communication system.

SUMMARY OF THE INVENTION

The disclosed embodiments provide a new and improved method for call recovery in a wireless communication system. According to one aspect, a method in a wireless communication system with a plurality of base stations, each of which has a set of neighbors containing neighboring base stations, each of the neighboring base stations having a default channel, transmitting default channel information to the mobile station; detecting a case initiating call recovery; and give the command to all base stations in the set of neighbors to transmit on the corresponding channels by default.

In one aspect, a wireless device includes an antenna; a processor associated with the antenna; a transmitting circuit associated with the antenna and the processor; a receiving circuit associated with an antenna and a processor; a first set of computer-readable instructions executed by the processor for receiving a list of neighbors of the base station, this list including default channel assignments for each of the neighbors; a second set of machine-readable instructions executed by the processor to identify the case initiating call recovery and block the transmission chain in response; and a third set of computer-readable instructions executed by the processor for establishing a handover to at least one of the neighbors.

In another aspect, the wireless device includes a transmit chain; a recovery adjustment unit configured to function after the call recovery operation to generate a predetermined power control command; and a power adjustment unit coupled to the recovery adjustment unit and the transmitting circuit, wherein the power adjustment unit is adapted to regulate the transmitting circuit in response to the power control command.

In yet another aspect, a computer program is embodied on a computer-readable medium comprising computer-readable instructions, the program including a first set of instructions executed to identify a special event; a second set of commands executed to prohibit call recovery during a special event; and a third set of instructions executed to notify the wireless communication system of the special event.

Brief Description of the Drawings

The signs, objectives and advantages of the disclosed method and device will become apparent from the detailed description below, taken in conjunction with the drawings, in which the same reference position are indicated respectively throughout the description and on which:

FIG. 1 illustrates in block diagram form a wireless communication system according to one embodiment;

FIG. 2 illustrates in block diagram form part of the wireless communication system of FIG. 1 according to one embodiment;

FIG. 3 illustrates in timeline form the signal quality of two base stations in the wireless system of FIG. 2 according to one embodiment;

FIG. 4 illustrates in block diagram form part of the wireless communication system of FIG. 1 during recovery according to one embodiment;

FIG. 5 illustrates, in a timing diagram, the signal quality of two base stations in a wireless communication system according to one embodiment;

FIG. 6A and 6B illustrate, in a flow chart, a method for recovering a call at a base station according to one embodiment;

FIG. 7A and 7B illustrate, in a flow chart, a method of call recovery at a mobile station according to one embodiment;

FIG. 8 illustrates in block diagram form the architecture levels in the system of FIG. 1 according to one embodiment;

FIG. 9 illustrates in a time diagram a call recovery operation in the system of FIG. 1 according to one embodiment;

FIG. 10 illustrates, in a timing diagram, the initiation of a transmit power level in a mobile station following call recovery according to one embodiment of the present invention; and

FIG. 11 illustrates in block diagram form the operation of a wireless device in the system of FIG. one.

Detailed Description of Preferred Embodiments

A call recovery method in a wireless system according to one embodiment provides information regarding cells in neighboring and / or sectors that are available and capable of recovering a call for a mobile station that is at a potential risk of losing a communication line. Each of the base stations capable of restoring a call has a direct default call recovery channel, identified by a given code. In another embodiment, more than one direct default call recovery channel is assigned to one neighbor, and the mobile station uses a hash function with MIMS (International Identification of Mobile Stations) (IMSI), VMIMS (Temporary International Identification of Mobile Stations) (TIMSI), EPN ( electronic serial number) (ESN), system time, or a combination thereof, to specifically decide which channels to use to receive transmission from each base station capable of reconnecting a call. The mobile station then uses this channel to receive signals from the reconstructing base station. The mobile station may be instructed to combine the power control subchannels from a plurality of neighboring recovery base stations via overhead messages when the mobile station accesses the base station. This can also occur when the mobile station moves to the coverage area of the base station, while the mobile station is in an idle state (standby state), i.e. without permanent communication lines, through messages on traffic channels when a call is initiated or during a handover, when the active set changes for the mobile station.

FIG. 1 illustrates a wireless communication system 10 with a plurality of cells 12, 14, 16, 18, 20, 22, 24. Cells 12, 14, 16, 18, 20, 22, 24 communicate with the BSC 26 over the air radio interface. Each of the cells 12, 14, 16, 18, 20, 22, 24 has a corresponding set of neighbors composed of cells in a geographical neighborhood and / or transmission neighborhood. For example, cell 18 has a set of neighbors including cells 12, 14, 16, 20, 22, 24. In spread spectrum transmission systems, such as Code Division Multiple Access (CDMA), defined as “ The compatibility standard for a mobile station — the TIA / EIA / IS-95 base station for a dual-mode spread spectrum cellular system ”, hereinafter referred to as the“ IS-95 standard ”, or the“ TIA / EIA / IS-95 standards for spread spectrum CDMA 2000 systems ”, Hereinafter referred to as“ CDMA2000 standard ”, spread spectrum signals occupy the same channel frequency band, and each signal has its own different pseudo-noise (PN) (PN) sequence. The operation of the CDMA system is described in US Pat. No. 4,901,307, entitled “Extended Spectrum Multiple Access Communication System Using Satellite or Terrestrial Repeaters,” as well as in US Pat. to which the applicant belongs to this patent application and which are expressly incorporated here by reference. Moreover, many users transmit messages simultaneously in the same channel frequency band.

FIG. 2 illustrates part of the system 10 of FIG. 1, including a base station 32, labeled BS1, communicating with MS 38. BS1 32 is located in cell 18 of FIG. 1. Two other base stations 34, 36, labeled BS2 and BS3, respectively, are in cells 16, 24, respectively. The airborne radio interface provides the environment for the forward link (PL) (FL) for transmissions from BS1 32 to MS 38 and the reverse link (OLS) from MS 38 to BS1 32. Note that MS 38 can move in system 10 so that the quality signal to BS1 32 and from it deteriorates. To start a call, the MS 38 sends transmissions on the access channel. BS1 32, BS2 34 and BS3 36 send channel assignment messages on the paging channel. The channel assignment identifies the Walsh code metric for each base station.

Signal quality is generally measured as the signal-to-noise ratio (SNR) (SNR) and can be expressed as the energy of the pilot signal per elementary signal to the total received power density (E _C / I ₀ ). FIG. 3 illustrates a graph of signal quality measured at MS 38 for BS1 32 and BS2 34. The signal quality for BS2 34 begins to increase at time t0 and continues to increase above the threshold level marked P_DOP after time t1. The threshold level P_DOP ensures the quality of the reference signal, above which the MS 38 is instructed to notify the base station to add the base station to its active set (AN) (AS). AN is made up of base stations that actively communicate with MS 38 both for transmission and reception. AN is usually selected from the base stations that are in the candidate set (CS) (CS). KN includes base stations that are candidates to become active liaisons with MS 38. KN is usually selected from base stations in a set of neighbors (NS) (NS).

In FIG. 3, while the signal quality from BS2 34 is improved, the signal quality from BS1 32 is degraded. An increase in the energy level of signals received from BS2 34 is added to the deterioration of signals from BS1 32, because The signal quality for a given base station is a comparison of the signal energy from that base station with all other available signals. At time t1, the MS 38 measures the signal energy from BS2 34 in excess of P_DOP. This indicates to the mobile station 38 that a corresponding action is required, i.e. this is the case of starting a handover. At time t2, MS 38 transmits to BS1 32 and BSC 26 a pilot signal strength measurement (SIPM) message (PSMM) containing measurement information for both BS1 32 and BS2 34. At time t3, BSC 26 establishes a communication line from BSC 26 to BS2 34 for MS 38. KBS 26 contains a selector. BSC 26 establishes a communication line forming a “reverse delivery” communication network between BS1 32, BS2 34 and BSC 26 with respect to MS 38. At time t4, BS1 32 sends a message about the direction of transfer of service (SOP) (HDM) containing information identifying BS1 32 and BS2 34 and their associated code pointers for forward link channels (PLC) from BS1 32 and BS2 34. This information allows the MS 38 to receive and demodulate signals from both BS1 32 and BS2 34. At time t5, MS 38 receives SNP from BS1 32 and begins to demodulate signals from BS2 34 in addition to signals from BS1 32. Note that in this example there is only one base station involved in handover. However, there can be any number of base stations involved in such a handover situation, and these base stations communicating with the MS 38 form an AN. When the MS 38 receives signals including symbols from a plurality of base stations in the AN, the MS 38 can combine these signals, resulting in a stronger signal. The combining process is called “soft combining” of the PLC and is usually performed when combining in the optimal ratio, i.e. with weighting based on signal quality. At time t6, the MS 38 sends a notification to the SOP, received from BS1 32 or a message about the completion of the transfer of service (SZP) (NSM), indicating the successful completion of the transfer of service.

In FIG. 3, a situation may arise in which the signal quality of BS2 34 increases too quickly. In this case, the signal level BS2 34 relative to the signal level BS1 32 contributes to the deterioration of the signal quality BS1 32. MS 38 is kept by the infrastructure from communication to receiving information necessary for transmission service, such as the shift of pseudo random noise (PN), necessary to identify BS2 34 or the channel used by BS2 34 for MS 38.

In a typical CDMA handover process, when a mobile station moves from the coverage area of one base station to the coverage area of another base station, the handover prevents link loss. In one type of handoff, soft handoff, the mobile station simultaneously supports connections to two or more base stations. The current location of the mobile station can be considered as the source cell, while the next cell into which the mobile station moves can be called the final cell. The mobile station uses a comb-type receiver (rake receiver) to demodulate a plurality of signals received on the PLC from a plurality of base stations. The two signals combine to give a composite signal with improved quality. Although each of the many base stations involved in soft handoff demodulates the received signal separately, each sends demodulated and decoded information to the BSC. The BSC contains a selector that selects the best frame from the set of received frames. For many conditions and system requirements, other handoffs may be used.

In a handover assisted by a mobile station (POSM) (MANO), a mobile station performs signal quality measurement for PLC pilots from multiple mobile stations. This information is reported to the source base station. The signal quality is compared for different thresholds in order to make a decision to add base stations to the AN. If the signal quality of a given pilot signal is higher than the pilot detection threshold P_DOP, this pilot signal is added to the AN. In another embodiment, the pilot signal may be added first to the ST, and then to the AN. In fact, this threshold allows the state of the base station to be transferred from one set to another.

Call recovery provides information to the mobile station ahead of schedule in the event that handoff negotiation is not possible. Call recovery is initiated in different situations. In normal operation, the mobile station and the base station use triggering cases to determine their respective operation. For example, a mobile station operating in system 10 uses multiple thresholds to make decisions based on what information is reported back to the base station. One threshold discussed above, P_DOP, indicates a signal quality level for adding a base station to an AN. When a mobile station receives a signal that is measured above P_DOP, this mobile station moves this base station to the SC, more often searches for this base station and reports this condition to the system through its existing AN. Another threshold, P_ISCL, provides a quality signal level below which the base station will be excluded from the AN. When the mobile station receives a signal that is measured below P_INVAL for a time longer than P_TISCL, the mobile station reports this condition to the system through the existing AN. In each case, the base stations in the AN transmit this information to the base station controller.

To restore a call, the base station in the AN looks at any of the many possible triggering cases. The first type of cases initiating call recovery occurs when the signal quality of the PLC is lower than the threshold level for a longer time than for another threshold. This kind of triggering cases includes those when the base station receives constant power control (PA) (PC) requests from the mobile station to increase the transmission level at the base station. Often the base station is already transmitting to the mobile station at the maximum level of maximum power. For example, the transmission of PLC traffic is maintained at a high level for a given time interval. A mobile station can send many requests to increase power, i.e. TEAMS ABOVE. Alternatively, the mobile station may report an excess of erasures. Erasure occurs when a larger number than the threshold level of bits are received without confidence in the intended value. In another case, the mobile station transmits messages indicating to the base station that its external loop settings are high or at the maximum allowed level, or at these levels for a longer time.

The second type of triggering cases occurs when some response is expected from the mobile station, but no response is received or another response is received. This type of triggering event includes a lack of acknowledgment from the mobile station to a message sent by the base station that requires confirmation. This message may be sent a predetermined number of times before the trigger condition is satisfied. This predetermined number may be fixed or variable and variable over the air. Similarly, the base station can receive repeated OLS messages from the mobile station that require acknowledgment, these messages being received after the acknowledgment is transmitted by the base station.

The third type of triggering cases refers to the poor quality of the reverse link, for example, when the frame error rate (FER) in the OLS is above a threshold level. Alternatively, the OLS may be maintained at a high level for a predetermined time interval. But another situation may have a high setting of OLS. The base station to be added to the AN also has cases initiating call recovery that initiate a recovery action. The most important triggering case is a notification from the BSC that there is a potential problem with a given mobile station. In this case, the base station starts searching for signals from this mobile station.

The mobile station may also use various cases initiating call recovery to enter call recovery. The first type of triggering cases occurs when there is an abnormal number of errors in the received signals. For example, erasing PLCs on a moving window may exceed a predetermined threshold level. In one embodiment, this threshold level is 12 consecutive frames experiencing erasure. In this case, the mobile station will turn off the transmitting part of the mobile station and may turn on the transmitter again when at least two consecutive PLC frames have not been erased.

A second type of recovery-triggering case for a mobile station occurs when the mobile station receives UM commands from the base station instructing to increase power. The base station may have difficulty receiving OLS signals due to large path loss from the mobile station.

A third type of recovery initiating case occurs when one or more OLS messages that require confirmation from the base station are not acknowledged. This is called a case that triggers a retransmission attempt. Similarly, there may be an incorrect response or there may not be a response from the base station to a message from the mobile station. A similar type of triggering event occurs when receiving repeated PLC messages requiring confirmation, after the mobile station actually transmits the confirmation.

A fourth type of triggering recovery event occurs when the mobile station transmits at a high level for a predetermined time interval. It is assumed that the OLS does not go to the base station with sufficient energy.

In one embodiment, flexible thresholds are implemented for one or many different cases that trigger call recovery. These call recovery triggering cases may be based on a plurality of attempts to transmit in system 10. These attempts are often performed at the link level between the signal and physical links. The link layer is called layer 2 and is discussed below with respect to FIG. 8. In recoverable systems, such as system 10 of FIG. 1, the MS 38 performs a recovery procedure to support a call when a communication link, such as a PLC, is degraded. A triggering case often initiates a restore operation, and this triggering case indicates when a parameter or metric crosses a threshold. These thresholds can be dynamic, adapting to the conditions of the system 10 and the environment. Similarly, thresholds can be adjusted based on a history or statistical record of the functioning of the system 10.

In one embodiment, the number of OLS retransmissions, or the time between successive erasures, or the transmitter being turned off in the MS 38 may occur in response to a command transmitted from the infrastructure of the system 10, such as BS 32 and / or BSC 26. In an alternative In an embodiment, a fixed parameter is determined for a particular action, for example, a specific maximum number of allowed retransmissions. In another embodiment, the condition and / or location of the mobile station determines the triggering case. The proximity of the current transmission level of the MS 38 to a predetermined maximum value may trigger call recovery. Other triggering cases include the quality of the submarine, measured by the erasures of the transmissions in the current AN, the lack of in-loop power control, and what is desirable for the MS 38 SNR differs from that provided by the internal circuit, etc., other variants of execution may combine a specific parameter and the condition of the mobile station as a triggering case.

The infrastructure of system 10 can provide the MS 38 with operational-type information useful in determining the thresholds for triggering call recovery cases, and can use this information when selecting the fixed parameters provided for the MS 38 to use as thresholds for the triggering case. In one embodiment, a typical number of call retries that have difficulty or are excluded. An alternative embodiment utilizes an OLS boot to set and adjust thresholds. Alternative embodiments may use the location of the MS 38 in the system 10, such as a sector of a given cell. Other embodiments consider a day of the week and / or time of the day in conjunction with known patterns of mobile traffic. A combination of any of these mechanisms may also be embodied when applicable or necessary.

In the system 10 of FIG. 1 and 2, each base station 32, 34, 36 transmits additional overhead information to the mobile stations with which it communicates. This additional overhead information for each BS 32, 34, 36 includes its corresponding list of neighbors. This list of neighbors identifies the corresponding shifts of the pseudo-random noise (PN) code of the neighbors.

In FIG. 4, BSC 26 responds to any of a variety of triggering cases by establishing a reverse delivery connection with BS1 32 and BS2 34. In accordance with one embodiment, the call recovery method 100 is initiated, as illustrated in FIG. 6. A specific signal quality graph for one example is illustrated in FIG. 5. In this example, there is time to identify the MS 38 as having a potential problem.

In the call recovery method 100 of one embodiment shown in FIG. 6A and 6B, in operation 102, BS1 32 sends default channel assignments to the MS 38 for a set of neighboring base stations. Base stations in a neighbor set are recoverable blocks having the necessary software and / or hardware to implement call recovery and having coverage area (s) that overlap such a zone of a base station sending a set of neighbors. The default channel assignments identify the default channel code pointer used by base stations in a set of neighbors, including the code for BS2 34. Each of the base stations in a set of neighbors capable of restoration has an extended default code that will be used to identify a mobile station in need of call recovery. This extended code in one embodiment is a specific Walsh code. BS2 34, at operation 104, sends a case to MS 38 that triggers retransmission attempts. This case, which starts the attempt to repeat the transmission, dictates the number of attempts that is allowed for the MS 38 before initiating call recovery operations. Then BS1 32 determines in the decisive rhombus 106 whether a recovery triggering event has occurred. If the recovery triggering event does not occur, processing waits for the triggering event to occur. When a triggering event occurs, processing continues at operation 108 to instruct all base stations in the NS for BS1 32 to transmit on their default channels corresponding to MS 38. Note that some of the base stations in the NS may be unable to establish a communication line due to weakness PLC or OLS, however, each base station in the NS starts transmitting to MS 38. Many transmitters provide a stronger PLC signal to MS 38 and a more reliable OLS to BSC 26.

Note that according to the present embodiment, the number of attempts to transmit an OLS message or the amount of time allowed for successive erasures is determined in the BSC 26 and provided to the MS 38 through messages and broadcasting over dedicated radio links. An alternative embodiment uses a fixed parameter, different from the rest of the parameters. One embodiment includes a mobile conditions feature. Mobile conditions may take into account how close the actual transmission level of the MS 38 is to the maximum transmission level. Similarly, another mobile condition takes into account the quality of the OLS, such as erasure in the current AN. Another mobile condition takes into account in-circuit shortages. This in-loop shortage is the difference between a given SNR and an SNR delivered by an in-loop power control. Another embodiment combines a mobile condition with a transmission type.

The allowed number of attempts can be adjusted according to statistics related to missed calls or challenges with difficulties. For example, there may be an average number of attempts, above which most challenges with difficulties are not restored. Other considerations include loading the OLS, location of the MS 38 and / or time of day or date. In the latter case, some mobile traffic patterns affect the number of mobile stations requiring quick call recovery.

Returning to FIG. 6A, BSC 26 determines the current AN for the MS in step 110. Then, BSC 26 initiates an SOP timer in step 112 and transmits the SSC in step 114. At this point, system 10 wants to move the communication links from the default channels. These channels are by default available for use by any of the mobile stations in system 10, and therefore their use should be optimized. Since the MS 38 uses the default channel, this channel is not available for use by another mobile station. The base stations in the NS are instructed to initiate transmissions on the alternative or new channel in parallel with the transmissions on the default channel. This is the initiation of a handover condition.

If the BSC 26 in the decision diamond 118 received a message from the MS 38 indicating that the handover has been completed, processing continues at operation 120 to disconnect the communication links of the MS 38 with the members of the National Assembly on the default channels. Then, processing continues at operation 124. In contrast, if a handover completion message is not received, BSC 26 checks in decision diamond 122 whether the SNP timer has expired. If the SNP timer has expired, the corresponding channel by default completes the transmissions to the MS 38, call recovery is canceled at operation 124, and the use of both the default channel and the new channel is terminated at operation 125. Normal operation is restored at operation 126. If in the decision diamond 122 the timer has not expired, the processing returns to waiting for the message about the completion of the handover from the MS 38 in the decision diamond 118.

FIG. 6B details a part of method 100 that illustrates step 110 as initiating a timer in step 130. BSC 26 checks the CIMS in decision diamond 132. If accepted, the processing continues at operation 134 to establish an AN to include neighbors included in the CMSP. If the IMSC is not accepted, processing continues at decision diamond 138 to determine if the timer (initiated at operation 130) has expired. If the timer has expired, processing continues in the decisive diamond 144. If the timer has not expired, processing returns to the decisive diamond 132.

After the AN is installed in operation 134, if the OLS is to be improved in the decisive rhombus 136, the BSC 26 determines whether there are any neighbors not included in the SIWP that received the signal (s) of the MS 38 in the decisive rhombus 140. These neighbors are called listening neighbors (CC) (HN) and are added to the AN in operation 142. Then, the processing returns to operation 112 of FIG. 6A.

If the timer expired without receiving the IMSC, the BSC 26 determines in the decision diamond 144 whether there are any neighbors who received the signal (s) of the MS 38 OLS, i.e. SS. In this case, the AN is established at operation 146 to include these SSs. If no SSs are found in the decision diamond 144, call recovery is completed at operation 148 and the call is completed.

In the decision diamond 110, the method determines whether the transmitter MS 38 is turned off. If this transmitter is turned off, the BSC 26 instructs the MS 38 to turn on the transmitter in step 110.

A mobile station call recovery method 200 for one embodiment is illustrated in FIG. 7. At operation 202, the MS 38 communicates with base stations in the AN (0). This identifies the current AN. If the recovery-triggering event occurred in the decision diamond 204, processing continues to the decision diamond 208. The recovery-triggering case may be one of those discussed above, or an alternative indication that the MS 38 requires an operation such as disaster recovery, i.e. MS 38 is likely to lose the PLC link. If no triggering event occurs, normal operation continues at operation 206. Decisive diamond 208 determines whether the transmitter is allowed to operate in the MS 38. If the transmitter is enabled, processing continues at operation 214, and if not, the MS 38 checks the condition of the triggering case in the crucial rhombus 210. If a trigger condition exists, this indicates that the MS 38 should prohibit (block) the operation of the transmitter, then, at step 212, the corresponding action is taken, and processing continues at step 214. From The absence of a triggering event indicates that the operation of the transmitter should be prohibited, then processing continues at operation 214. At operation 214, a standby timer is set. This wait timer is checked in decision diamond 216, and the recovery timer expires at step 218. If the wait timer has not expired, processing continues in decision diamond 222 to determine if the MS 38 has returned to normal operation. Normal operation continues from operation 206, otherwise processing returns to waiting for the wait timer to expire.

Next, in FIG. 7, from step 218, if the transmitter in the MS 38 is locked, in step 220, the transmitter is unlocked. The MS 38 transmits the predetermined header during the time interval Y. This header provides transmission information for the MS 38, not the actual data or symbols. The MS 38 transmits the SIPM information at operation 228. In the decisive diamond 228, if an SOP is received or if some notification confirming the SIPM is received, the MS 38 proceeds to wait for a predetermined time interval X, after which the AN is updated. If neither SOR nor SILC is received in decision diamond 230, processing continues in decision diamond 232 to verify that the SIPS has not been transmitted more than the maximum allowed number of times. If SIUP can be sent yet, i.e. the maximum is not reached, the processing returns to operation 228, and the CIMS is sent again. However, if the maximum is reached, processing continues at operation 236, and call recovery is terminated.

According to an alternative call recovery method, BSC 26 notifies all of the BS1 32 neighbors capable of restoration to a potential problem. The BSC instructs the MS 38 to turn on the transmitting part of the MS 38 and instructs the base station (s) in the set of neighbors to listen to the MS 38. When a signal is detected or requested from the MS 38, each base station in the set of neighbors transmits a report. Reports are received from a subset of base stations, and this subset may include all base stations in a set of neighbors or part of base stations. BSC 26 notifies the MS 38 of the default channels of each base station in this subset. The subset base stations then use the appropriate default channel to initiate communication with the MS 38.

In yet another method, a subset of a set of neighbors is determined based on the latest transmitted SIPM. The problem is that the last transmitted SIPM may be received incorrectly, in which case the SIPM used to identify the subset is incorrect. As an example, when the last received SIPM identifies BS1 32 and BS3 36, and MS 38 sends a subsequent SIPM identifying BS1 32 and BS2 34 that was not received, call recovery is broken. BSC 26 sets up a reverse delivery network with BS3 36, and BS3 36 starts transmitting to MS 38 on the default channel. Unfortunately, MS 38 assumes that communication will be established with BS2 34 to restore the call, and is prepared for exclusion on another channel by default. Excessive transmission from BS2 36 is wasted and effectively creates more noise in system 10.

When call recovery is initiated by the mobile station 38, a timer may be used to delay such initiation following the event initiating call recovery. The time interval of the timer can be set by the BSC 26. After this timer, the MS 38 transmits a header on the channel of the pilot signal of the OLS. This header includes a call recovery message. In one embodiment, the header is a predetermined constant that can be set by the base station controller 26. In an alternative embodiment, the header has a variable length defined by the system operator. Following the transmission of the header, the MS 38 sends a message regarding the change (s) of the PLC. This message may be a pilot signal strength measurement (SIPM) message. This message can be sent several times to guarantee reception by the second base station BS2 34.

Combinations of the above methods provide various benefits for call recovery. In one embodiment, a call recovery method is based on a radio environment of a base station of a source cell. When the number of neighbors that are able to reconnect is small, for example 2, KBS 26 instructs all neighbors to transmit on the corresponding channels by default. The AH is updated, and the MS 38 transmitter is unlocked without delay. For larger sets of neighbors that are able to reconnect, BSC 26 instructs neighbors to listen to signals from MS 38. After a delay spent waiting for neighbors to report whether they can receive signals from MS 38, to those that hear neighbors, give the command to use the default channels. Similarly, if the CIDM is received from the MS 38 in a predetermined time interval, the base stations identified by the CIDP are instructed to use the default channels. Note that when the PLC works properly, which is determined by a fixed number of consecutive frames, the commands of the PA sent through the subchannel of the PA are considered reliable.

FIG. 8 illustrates the architecture of the wireless communication system 10 of FIG. 1 in a layered format format. Architecture 700 includes three layers: a signaling layer 702, a link layer 704, and a physical layer 706. The signaling layer 702 provides top-level signaling 708, data services 710, and voice services 712. Signaling layer 702 provides voice, packet data, simple circuit data, and simultaneous voice and packet data services. Protocols and services are provided at this level, corresponding to the two lower levels. The link layer 704 is subdivided into a Link Access Control (LAC) sublayer 714 and a Media Access Control (MAC) sublayer 716. The applications and protocols of signaling layer 702 utilize the services provided by UDL layer 714. The link layer 704 serves as an interface between the upper layer protocols and the applications of the signaling layer 702 and the physical layer 706. The MAC sublayer 716 further includes a Quality of Service (QoS) multiplexing and delivery unit (QoS). The link layer 704 links the signaling layer 702 to the physical layer 706. The physical layer 706 is made from the physical transmission channel 724.

FIG. 9 provides a timing script for operating the system 10 of FIG. 1 according to one embodiment. Reference is made to the methods of FIG. 6A, 6B, and 7. The horizontal axis represents time, and the vertical axis represents different channels used for transmission. The base station of the source cell BS1 32 is provided in the middle, and the information is transmitted over the traffic channel to the MS 38. For the MS 38, two channels are shown: the transmission channel Tx and the reception channel Rx. Two scenarios are shown for the receive channel: Rx ₁ and Rx ₂ . Also shown is a neighboring base station, which is the terminal base station, BS2 34. Both the default channel and the new channel are illustrated. The new channel is a channel to be used for communication with the MS 38 after a handover. Processing begins with the MS 38 receiving transmissions from the first AN identified as AN (0). MS 38 simultaneously transmits on the traffic channel for BS1 32 the source cell. At time t1, a case occurs that triggers a call recovery. Both MS 38 and BS1 32 recognize this triggering case. Note that the triggering case may be a general case, such as continuous PA requests from MS 38 in BS1 32 to increase transmit power in the PLC, or may be separate cases for MS 38 and BS1 32. In addition, MS 38 and BS1 32 can Do not recognize the triggering case (s) at the same time. Often, the MS 38 may be in position to recognize a triggering case up to BS1 32 during PLC failures.

When the triggering case is identified at time t1, BSC 26 initiates a default channel transmission from neighboring BS2 34. At time t2, BS2 34 starts transmitting on the default channel to MS 38. This transmission occurs in parallel with the same transmission from BS1 32. When occurs triggering case, the MS 38 locks the transmitter for a predetermined waiting time interval. At time t3, the wait interval ends and the MS 38 transmits the header during the time interval Y. At the same time, the AN in the MS 38 changes from AN (0) to AN (1). The base stations identified in AN (1) are all base stations listed in the latest SIUP. In an alternative embodiment, AN (1) may be a set with all neighbors for BS1 32 and BS1 32 itself.

At time t4, the header is completed and the MS 38 begins to transmit the current SIUP. In response to the reception of the CIMS at time t5, BS1 32 and BS2 34 transmit the DSS at time t6. SNP signals the change of AN to AN (2) at time t8. Note that the next SIPM is sent at time t7, and the SIPM is sent periodically to identify the signals received in the MS 38.

At time t8, BS2 34 starts transmitting on a new channel for MS 38. MS 38 transmits DSS, which starts the completion of transmissions for MS 38 on the default channel at time t9. In one embodiment, the DSS is transmitted periodically or continuously until their correct reception is confirmed by the base station. In the scenario illustrated in FIG. 9, call recovery starts at time t2 and ends at time t9. At time t9, the handover ends, and BS2 34 is the current base station of the source cell for MS 38.

An alternative scenario is illustrated for the Rx ₂ receive channel. Here AH (0) remains active until t5. Following time t5, the MS 38 continues to receive from AN (0) for a predetermined time interval X, after which there is a change to AN (1). This provides additional time for the base station side to determine a subset of BS1 32 capable of reconnecting to the neighbors for transmission to MS 38 for recovery. At time t8, the next change occurs in response to SOR from AN (1) to AN (2). This scenario corresponds to a method in which only those neighbors that are able to receive signals from the MS 38 are instructed to transmit through the corresponding default channels.

Upon completion of call recovery and completion of handover, the MS 38 should determine the initial transmit power level. According to one embodiment, the system 10 of FIG. 1 uses a closed loop power control (feedback system) to control transmit power levels. Alternative embodiments may use the additional open loop power control method (open loop system). An open loop refers to operation controlled by a transmitter (or a mobile or base station) when the receiver is not directly involved. For example, a particular reverse link open loop power control refers to a mobile station to adjust the transmit power of the reverse link based on the power level of signals received from the base station on the forward link. Closed loop power control extends the open loop operation, as a result of which the receiver is actively involved in deciding on power control. For example, to control the power of the closed loop OLS, the base station compares the power level of signals received from a given mobile station with a threshold value. The base station then instructs the mobile station to increase or decrease the transmit power of the reverse link based on this comparison. On the contrary, the mobile station monitors the power level of signals received by the PLC, and provides feedback on the quality of the PLC for the base station. Closed loop operation is used to compensate for power fluctuations associated with fading, such as Rayleigh fading, of a given communication line.

Immediately after the standby timer expires and before the establishment of power control, the MS 38 starts transmitting at the initial power level. The transmit power level of the OLS can be resumed from the one that was immediately before the MC 38 transmitter was blocked. The power level can remain at this initial level until closed-loop power control resumes.

In an alternative embodiment, the power level is initiated at the last level before the transmitter is blocked, and then gradually increases at a given speed until closed-loop power control resumes. The increase rate is usually set by BS1 32 and / or BS2 34 and may be fixed or variable. These increases continue until closed loop power control resumes.

Another embodiment starts recovery by open loop control based on the total received power in the frequency band. This procedure is similar to the access procedure defined in IS-95 and IS-2000. This can be adjusted for multiple forward link base stations visible on the MS 38. Open loop control continues until closed loop power control resumes. FIG. 10 illustrates power control according to this embodiment. The horizontal axis represents time, and the vertical axis represents transmission power level. At the first moment t1, the transmit power is at the initial power level. After the first time interval at time t2, the transmit power increases by a predetermined increment. This increment value can be a fixed value or it can be a variable that increases or decreases with increasing time. In one embodiment, the increment value is adaptive and responds to the conditions of the system 10, wherein the increment value can increase or decrease from one time interval to a subsequent time interval. Finally, a predetermined maximum transmission level may be achieved after a predetermined number of time slots. Then, the transmit power is at its limit value awaiting the resumption of closed loop power control.

In yet another embodiment, the initial transmit power is based on the quality of the received pilot signals. The quality of the signals is measured by the ratio E _C / I _{0 of the} pilot signal or the value E of _the pilot signal for the intended AN. In open loop power control, transmit power typically has a ratio defined as:

where k is a constant, T _x is the transmission energy of the OLS, and R _x is the received PLC energy. For a closed loop power control method, transmit power typically has a relationship defined as:

and y (t) is the cumulative correction variable based on all valid power control commands received up to time t. The expression (k + y (t)) is denoted by β. In an alternative form, the following relation is true:

Determining the initial transmit power applies the value β of previous gears to new gears. A new transmit power level is calculated while:

where T _x (0) is the transmission energy before the call is restored, R _x (0) is the reception energy before the call is restored. In this case, the transmit power is adjusted according to the previous ratio of the transmit power level to the receive power level.

Wireless MS 38 operating in system 10 of FIG. 1, for example, a cell phone or personal digital assistant (PDA), is illustrated in FIG. 11. The MS 38 includes an antenna 300 for transmitting and receiving. An antenna 300 is coupled to a duplexer 302 to isolate the receive path from the transmit path. The duplexer is connected to a receiving circuit 308 forming a receiving path, and is connected to an amplifier 304 and a transmitting circuit 306 forming a transmitting path. An amplifier 304 is further coupled to a power control unit 310 that controls the amplifier 304. The amplifier 304 receives transmission signals from a transmitting circuit 306.

The received signals through the antenna 300 are supplied to a power control unit 314, which embodies a closed loop power control circuit. A power control unit 314 is connected to the communication bus 318. This communication bus 318 provides a common connection between the modules in the MS 38. The communication bus 318 is additionally connected to the memory 322 and the recovery control unit 316. A memory 322 stores machine-readable instructions for various operations and functions applicable to the MS 38. A processor 320 executes instructions stored in the memory 322. For normal operation, the power control unit generates a PA signal for power control unit 310 via multiplexer 312. Power control unit 310 then transfers the PA signal as the gain level to amplifier 304.

When call recovery occurs, the MS 38 may block the transmitter. When the transmitter is unlocked, a handover complete signal is supplied to a recovery adjusting unit 316. This handover complete signal instructs the recovery control unit 316 to generate a predetermined PA signal. The UM signal generated in this way can implement any of the schemes for generating the initial transmit power of the OLS discussed above, or it can implement an alternative method. The handover completion signal is also provided to the multiplexer 312. Following the call recovery, the PA signal generated by the recovery control unit 316 is sent to the power control unit 310. In parallel, closed loop power control begins. When closed loop power control is fully resumed, the handover complete signal is canceled, and multiplexer 312 selects the PA signal generated by power control unit 314 to supply it to power control unit 310. The operation of the recovery control unit 316 may be performed by a microprocessor 320 operating on program instructions, or may be embodied in apparatus for efficient and reliable operation.

In one embodiment, specific operations of MS 38 or BS1 32 are considered special events. These special events include many conditions and procedures that can trigger triggering events. In other words, special events can give rise to a situation where a case initiating call recovery occurs, but the call is not suppressed. One special event is the search for the location locator of the mobile station. MS 38 is instructed to look for an alternative frequency signal global positioning system (GPS) (GPS). The GPS provides the location of the MS 38 or partial location information of the MS 38. The location locator of the mobile station is searched periodically or aperiodically. Typically, MS 38 has a priori information regarding the timing of such searches. Other events may include searching for candidate frequencies in preparation for inter-frequency hardware handoff, when the mobile station tunes to a different frequency in order to search for a signal from base stations at a different frequency.

Other events may include actions performed by the MS 38 at a time when the triggering event should be ignored. In the events of these types, the MS 38 notifies BS1 32 of the source cell of a special event. In one embodiment, the special event is the search for a candidate frequency, while the MS 38 tunes to a different frequency to view signals from neighboring base stations at that frequency. This provides a better transfer between coatings at different frequencies, for example, switching between the frequency of the personal communication system (PCS) (PCS) and the cellular frequency. When this type of special event is triggered by the mobile station, the MS 38 notifies the BS1 32 of the source cell to ignore triggering cases with respect to the MS 38 for a specific time interval or until further notice.

According to one embodiment, in order to avoid such false starts during special events, the base station of the source cell, such as BS1 32, gives permission to this event and notifies the MS 38 of the timing of this event, including at least when this event should start, and the length of time allotted for this event. The MS 38 and the base stations in its AN are prohibited from initiating call start (s) during a special event.

In an alternative embodiment, MS 38 notifies BS1 32 of a special event or set of these special events. In response to this notification, BS1 32 may authorize a special event, prohibit this event, or reschedule this event. Again, this provides the MS 38 and the base stations in its AN with enough information to block call recovery starts during a special event.

Thus, a new and improved method for maintaining communication in a wireless communication system is presented here. When the communication line between the mobile station and the corresponding base station of the source cell is disrupted, the mobile station and infrastructure pre-sets potential disaster recovery base stations. The base station of the source cell is in contact with all neighbors capable of reconnecting the call as potential disaster recovery stations. A call-retrieval neighbor has a default channel configured to soft handoff to a mobile station. This default channel is only used temporarily during the initial part of the handover. Each disaster recovery base station is instructed to use the default channel for disaster recovery transmissions. Disaster recovery transfer is considered a call recovery operation. The mobile station establishes a soft handoff with the disaster recovery base station, while the PLC uses the default channel. The disaster recovery base station then initiates transmissions on the alternate channel. When the handover is completed, the disaster recovery base station stops using the default channel with respect to transmissions to the mobile station. In one embodiment, the base station of the source cell supplies the mobile station with a list of capable of reconnecting neighbors as backup during transmissions and before resolving the communication line problem. In this case, for situations in which the PLC is lost before receiving the handover information, the mobile station has sufficient information to complete the handover.

In an alternative embodiment, more than one default channel is assigned to neighboring BS2 34. Using multiple default channels or disaster recovery channels increases the call recovery capability of system 10. Each neighbor is then able to contribute to the call recovery of more than one mobile station, such as the MS 38. When operating, before the call is restored, BS1 32 of the source cell supplies the MS 38 an identifier corresponding to a plurality of channels associated with BS2 34. MS 38 and BS2 34 each store a determinative function, such as a hash function, to map identifiers to a particular channel. Using a hash function, in particular, is a pseudo-random procedure. In addition to this, the MS 38 is assigned an electronic serial number. The electronic serial number may be stored in the MS 38 or may be provided by the MS 38 upon call recovery. When a call is restored, BS1 32 of the source cell provides the electronic serial number of MS 38 in BS2 34. BS2 34 and MS 38 both use the specified function to calculate the appropriate default channel.

A hash function for the data structure allows you to recognize a keyword in a set of words with just one call to the data structure. The hash function maps its argument to the result of the specified type. A hash function is determinate and has no state. Those. the return value depends only on the argument, and equal arguments produce equal results. It is important for a hash function to minimize collisions, with a collision defined as two different arguments that are hashed into the same value. It is also important that the distribution of hash values is uniform; those. the probability that a hash function will return any particular value of a given type should, roughly speaking, be the same as the probability that it will return any other value. In alternative embodiments, other types of cryptographic functions may be implemented to identify multiple default channels for call recovery.

As examples, various illustrative logical blocks, modules, circuits, and algorithm operations described in connection with the embodiments disclosed herein may be embodied or executed by a Digital Signal Processor (DSP), Application Specialized Integrated Circuit (ASIC) , user-programmable logic array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, such as, for example, registers and elements with al a FIFO request processing algorithm, a processor executing a set of hardware and software instructions, any programmable software module and processor, or any combination thereof designed to perform the functions described here. The processor may advantageously be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The program modules may be located in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, ROM-CD (CD-ROM) or any other form of storage medium known in the art. The processor may reside in an ISDN (not shown). PSIS may reside on a telephone (not shown). Alternatively, the processor may reside in a telephone. A processor may be embodied in a combination of a DSP and a microprocessor, or as two microprocessors together with a DSP core, etc.

The previous description of the preferred embodiments is intended to enable a person skilled in the art to make or use the present invention. Various modifications of these embodiments will immediately be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without using inventive skills. Thus, the present invention is not intended to be limited by the embodiments shown here, but should be accorded the broadest scope consistent with the principles and new features disclosed herein.

Claims (2)

1. A wireless communication device for a CDMA communication system comprising a transmitting circuit, a power control unit coupled to the transmitting circuit, the power control unit being configured to control the gain of the transmitting circuit and the closed-loop power control unit, characterized in that it comprises a multiplexer and a call recovery adjustment unit, and the signal from the output of the power control unit in a closed loop is supplied to the power control unit through the multiplexer after canceling the completion signal I transfer service, which controls the multiplexer, which is also associated with the call recovery adjustment control unit, designed to generate a given power control command and configured to function when a signal is received to complete the handover. 2. The device according to claim 1, characterized in that the predetermined power control command is based on the transmit power level before the call is restored.

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